An LED backlight using an LED (Light Emitting Diode) as a light source has been adopted for recent liquid crystal display devices. Moreover, some of the recent LED backlights can control the light quantity for each of R (red), G (green), and B (blue) (or for each part thereof) individually, and can adjust a color balance of the backlight in addition to a brightness of the backlight.
The liquid crystal display device using the above-described LED backlight can generally change the brightness of the backlight to a brightness desired by a user, for example, based on a designation by the user. However, because the LED has an individual difference in an actual color or light quantity, the brightness or a color balance may be different for each backlight. Moreover, an output of the LED varies according to operating conditions, for example, the color changes and the light quantity decreases with an increase of temperature. Consequently, it is difficult to match the brightness of the backlight with the brightness desired by the user, by only a simple control based on the brightness designated by the user, independently of the individual differences and the operating conditions, without losing the color balance while mixing three colors of R, G, and B (more colors depending on the backlight).
As a method to solve the above-described problem, a method using a light sensor (color sensor) that can measure a light quantity for each color component (R, G, and B) included in received light has been proposed (for example, refer to Patent Document 1). The light sensor receives a part of light emitted from the backlight to measure the light quantity for each of R, G, and B of the light actually emitted by the backlight at a current time. A backlight (BL) control unit performs control (feedback control) to adjust drive conditions of the backlight sequentially, based on a light quantity measurement value for each of R, G, and B acquired via the light sensor.
FIG. 7 is a diagram showing a functional configuration of a liquid crystal display device according to the present invention. In FIG. 7, reference symbol 9 denotes a liquid crystal display device.
Hereunder, an example of a liquid crystal display device that performs feedback control by using the above-described light sensor will be described with reference to FIG. 7. As shown in FIG. 7, the liquid crystal display device 9 includes a backlight 90, a liquid crystal panel 91, a BL (backlight) control unit 92, and a light sensor 93.
The backlight 90 includes, for example, out of a R (red), G (green), and B (blue), a G LED light source and a B LED light source, and is an LED backlight for which it is possible to independently control a light quantity of G and a light quantity of B. In this case, a light quantity of R is uniquely decided incidentally based on the controlled light quantity of G and the light quantity of B.
The backlight 90 may be a backlight that includes LED light sources for each of R, G, and B for which it is possible to independently control each light quantity. Moreover, in this case, the backlight 90 may include a light source for other different colors in addition to R, G, and B.
The liquid crystal panel 91 is a functional unit that forms an image based on an image signal input from outside, and causes a viewer to visually recognize the image through light entering from the backlight 90.
The light sensor 93 is a digital color sensor that receives a part of the light emitted from the backlight 90, and outputs the light quantity for each of R, G, and B of the light as numerical values.
The BL control unit 92 performs control so as to match the brightness of the light emitted from the backlight 90 with a predetermined target brightness, by controlling the light quantity of G and the light quantity of B based on the predetermined target brightness. The target brightness is the brightness of the backlight 90, for example, designated by the user and desired by the user. Specifically, the BL control unit 92 receives a light quantity measurement value for each of R, G, and B acquired by the light sensor 93, and compares the brightness acquired based on the light quantity measurement value, with the target brightness desired by the user, and controls so that these agree with each other.
Brightness is generally expressed by a value acquired by multiplying each of the light quantity of R, the light quantity of G, and the light quantity of B respectively by a predetermined coefficient (respectively designated as r, g, and b), and adding the acquired values (r×R+g×G+b×B (R, U, and B are light quantities of respective colors)). For example, if the light quantity (per unit of time) detected for each of R, G, and B by the light sensor 93 is (R, G, B)=(95, 100, 90), the brightness of light is calculated by (r×95+g×100+b×90). The BL control unit 92 acquires the measurement value of the brightness by performing the above-described arithmetic processing using the light quantity measurement value for each of R, G, and B input from the light sensor 93.
Here, for example, even if the brightness calculated by (r×95+g×100+b×90) agrees with the target brightness, if the originally set color balance is (R:G:B=1:1:1), the condition to maintain the color balance is not satisfied. Consequently, the BL control unit 92 performs control to maintain the color balance (R:G:B=1:1:1), while adjusting the brightness of the backlight 90 to the target brightness based on the light quantity measurement value for each of R, G, and B input from the light sensor 93.
By realizing the above-described feedback control, the BL control unit 92 can perform control to adjust the color balance and to match the brightness of the backlight 90 with the brightness desired by the user, regardless of the individual difference of the backlight 90 and the operating conditions thereof.
As in the above-described liquid crystal display device 9, recently, a digital color sensor has been used as the light sensor for space saving and cost reduction. The general digital color sensor integrates each light quantity of the R component, the G component, and the B component of the light to be received, over a predetermined measurement time, and outputs the integrated value as a numerical value (digital value) after passage of the measurement time.